How much do we really gain from the A.I. rifles.

[J E Custom]

I like the idea of the AI cartridges was just wondering if we gained as much as we thought we did. I believe cartridges like the 220 Swift and tapered ones like that stand the most to gain in just plain old longer case life.

I will make an effort to explain what little I know about case life and throat erosion as related to the Ackley improved design.

A case with very little shoulder like the 220 Swift (21o) has pluses and minuses. The plus side is very easy extraction and feeding because of the taper. The minuses are based on the ignition process. cases with slight shoulder angles push more/most of the powder out of the case before it is completely ignited, causing faster throat erosion from the abrasive powder grains. the longer the powder stays in the case the better the throat life.

Cases with more shoulder angles (Like 35 to 40o)tend to hold the powder in the case longer and burn more of the powder inside the case minimizing the amount of un burnt powder that impacts the throat and lead angles. This Causing less throat erosion using the same amount of powder. The 40o shoulder also helps prevent the brass from flowing forward decreasing the case length growth and extending case life.

This was a big issue back when our powder selection was poor, and going to a 40 degree shoulder WAS A very measurable IMPROVENENT.
The only real downside that I can think of is the feeding/chambering of a round. The rifle must be set up correctly (Preferably with a center feed magazine) or feeding can be problematic

Now that we have a broader selection of powders we can improve the powder burn some , but the 30 to 40o shoulder still Improves the efficiency of the powder burn and in many cases actually improve it
even more.

In addition to all the pluses, more case capacity is another benefit.

J E CUSTOM

 

[HARPERC]

.....This was a big issue back when our powder selection was poor, and going to a 40 degree shoulder WAS A very measurable IMPROVENENT.......

The key word being measurable. Measurable meaning pressure, as well as velocity readings, side by side, same components etc.

One can look through the manuals, and find velocity differences comparing standard case to standard case, that exceed some of the claims for AI improved cases.

 

[ATH]

The key word being measurable. Measurable meaning pressure, as well as velocity readings, side by side, same components etc.

One can look through the manuals, and find velocity differences comparing standard case to standard case, that exceed some of the claims for AI improved cases.

We all know that manuals are based on the test platform and cover a wide range of variables...this is why we can't trust them and must work up.

Having shot a very large number of 243AIs and 243s, I can say it is a FACT that I have never come across a straight 243 that would come within 100fps of a 243AI of the same barrel length. Perhaps others have found fast barrels to make it so, but I have not. Run a 243 to 3200-3300fps with a 105gr and see how that brass looks afterwards. This is easy with the AI version.

Do you have a manual that shows a straight 243 load with a 105 at 3200+ fps? Comparing difference between manuals to the difference between straight and AI, without benchmarking that to a real world number, is meaningless. Because manuals show, say, a variation in 243 from 2950 to 3150 is not the same thing as a straight being quoted at 3050 and an AI at 3250.

 

[HARPERC]

.....We all know that manuals are based on the test platform and cover a wide range of variables...this is why we can't trust them and must work up.
..........Do you have a manual that shows a straight 243 load with a 105 at 3200+ fps? Comparing difference between manuals to the difference between straight and AI, without benchmarking that to a real world number, is meaningless. Because manuals show, say, a variation in 243 from 2950 to 3150 is not the same thing as a straight being quoted at 3050 and an AI at 3250.........

......The variables don't disappear just because they are provided by an individual.

.....Benchmarking to real world numbers is what I'm speaking of. Standardizing: powder lots, primers, brass, bullets, neck tension, chronographs, providing actual pressure data to accompany the velocity readings. Also having the same pre-determined end point using something more scientific than "sticky bolt lift" minus 1 grain.

 

[Capt RB]

The 2 major reasons for improving a case are reducing pressure and improving case life. The pressure aspect works like this. The straightening of the case wall allows the case to expand out instead of back. Think of a pipe thread. This is a tapered thread that tightens as it is screwed in because of the taper. A standard bolt is straight and tighens when it comes to a shoulder or bolt head. Loosen a pipe thread and it becomes easier the further you unthread the fitting due to the clearance. Whereas a standard thread is the same diameter from 1st to last thead.
Now when you apply this to a cartridge case. As the pressure builds a case with a larger taper will have less grip on the chamber wall. This will cause the case to have more thrust to the rear. This will show up as you reach max pressure in your velocity. The reason is in the amount of pressure wasted to bolt thrust because the case did not grip the chamber walls as well as a straighter case would.
You also see much more stable brass as an improved case expands out instead back reducing case stretch

 

[Wild Bill G]

The manual I was using is the latest Nosler from the looks of things all loads were shot using a universal reciever. Various barrel makes were used in the data but the barrels were all from well known makers. Universal recievers allow for pressure testing so one should assume a max load is a max load. This is not saying there is no room for some wiggle of powder charges.
As I have stated I am not against the AI cartridge imprvements I just always wondered how much we really gained. As well I have never chronographed my 30-06 AI against a normal 30-06 wich would be hard to do as my AI has a longer barrel than most 06 factory rifles.
JE gave some good info I had never even thought about with the shoulder angles. I am learning a llot as this discussion goes along. As we all know PO Ackley was a wild catter and with out them many of our favorite cartridges would not be around or not as quickly at least.

 

[Ksduckhntr]

I am having a 6.5 Swede built and go back and forth about AI'ing it. This will be a hunting rifle with a 22" barrel. If I AI'd this rifle from what I have read, it will become slightly more efficient thus allowing a slower pressure curve and extending brass/barrel life?

 

[tbrice23]

That sounds much more like a bullet failure than a cartridge failure. I don't care for the NBTs myself. Especially at hyper velocities unless shooting them at varmints. Throw a different bullet, and I bet your results are much better. 6mmAI should rock a deer with proper bullet construction and shot placement.

I've dispatched many whitetail with my 6AI. Try 105 gr vld at 3360! Most have 2" exits. I'm batting

1000 with mine.

 

[tbrice23]

Try 105vld at 3360 fps!
I'm batting 1000 with my 6AI

, most have 2" exit holes.

 

[Tidus56]

Try 105vld at 3360 fps!
I'm batting 1000 with my 6AIView attachment 90874 , most have 2" exit holes.

Nice! I wish I would have gone 6mmAI over my 243 AI.

 

[tbrice23]

Mine works well in a short action Savage. Even with VLDs seated to the lands.

 

[Tidus56]

Mine works well in a short action Savage. Even with VLDs seated to the lands.

Nice, my 243AI is in a savage short action with a stockade stock. I use mine for blowing up Prairie dogs with a 87 grain vmax. Its my overall favorite gun, but I could get even more destruction from the 6AI lol

 

[Pdvdh]

Don't have to worry about others using my ammo!

 

[jakelly]

AI just plain works. I've found if it's not showing a marked improvement, then slower powder needs used. I actually think it works a good bit better than it gets credit for.

I think improving the shoulder angle allows the use of even slower powders effectively. These powders don't burn the same way in every case. Today I'm using powders in cases that I would've thought way too slow when I started reloading. I don't use manuals much anymore either.